This invention relates to a local area network (LAN) path control system and, in particular, to an LAN path control system including a plurality of terminals each of which has two ports, an active port and a standby port.
A conventional duplex LAN system has duplicated LAN transmission lines, which are independent of each other. One of the duplicated LAN transmission lines is used for an active LAN system and the other is used for a standby LAN system.
Moreover, the conventional duplex LAN system includes a plurality of terminals each of which has duplicated ports. One of the ports is connected to one of the duplicated LAN transmission lines as an active port while the other is connected to the other of the duplicated LAN transmission lines as a standby port.
When the active port of a certain terminal fails, the terminal activates the standby port instead of the failed port. In this case, the other terminals must activate their standby ports and inactivate their active ports, because the active transmission line and the standby transmission line are independent of each other. Therefore, complicated processes and a long time are necessary to change from the active LAN system to the standby LAN system.
An LAN path control system is proposed to eliminate the need to activate the standby ports instead of the normal active ports of terminals that are unrelated to the failure.
The LAN path control system is used for a duplex local area network system including terminals each of which has two ports. One of the ports is used as an active port while the other is used as a standby port. The ports are connected to either a transmission line or transmission lines connected to each other.
The terminals are distinguished from one another by specific interact protocol (IP) addresses assigned to them. Moreover, the ports of the terminals are distinguished from one another by specific media access control (MAC) addresses assigned to them. Each of the terminals has a network information table for registering the MAC addresses of the active ports of the other terminals. Each of the MAC addresses is related with the IP address of the corresponding terminal in the network information table.
Now, consideration is made about a case where a first terminal, one of the terminals, transmits a packet to a second terminal, another one of the terminals.
At first, the first terminal refers to the network information table for the IP address of the second terminal before it transmits the packet to the second terminal. IF the IP address of the second terminal is found in the network information table, the first terminal reads out the MAC address connected with the IP address of the second terminal from the network information table. Then the first terminal transmits the packet to the second terminal by using the MAC address read out from the network information table. On the other hand, the first terminal asks the other terminals about the MAC address of the second terminal when the IP address of the second terminal is not found in the network information table. IF a reply including the IP address and the MAC address of the second terminal is transmitted from the second terminal, the first terminal registers a combination of the IP address and the MAC address of the second terminal in the network information table. Then the first terminal transmits the packet by using the MAC address of the second terminal. After this, the first terminal uses the MAC address registered in the network information table whenever it transmits another packet to the second terminal.
Each of the terminals stores combinations of the IP addresses and the MAC addresses of the other terminals to which it transmits packets like the first terminal.
In the meantime, each of the terminals must activate the standby port instead of the active port when a failure occurs in a path passing through the active port. In consequence, the specific MAC address of the active port related to the failure can not be used because the standby port has the specific MAC address different from that assigned to the active port. Accordingly, each of the other terminals must rewrite the network information table about the MAC address of the active port related to the failure.
A proposed LAN path control system has a problem that a long time and a complex process are necessary for rewriting the network information tables of the terminals.